Control system for fluid separation



April 21, 1964 E, A, HARPER CONTROL SYSTEM FOR FLUID SEPARATION Filed Aug. 23, 1962 mZON INVENTOR.

E A HARPER l W f ATTORNEYS United States Patent Oiice 3,130,027 Patented Apr. 21, 1964 3,135,627 CONTROL SYSTEM FR Film SEPARATION Ernest A. Harper, Eartiesvie, Ghia., assigner to Philiips Petroieum Campari* a corporation of Delaware Fiied Aug. Z3, i952, Ser. No. Zl 9 Claims. (Cl. 62-2l) This invention relates to method and apparatus for separating gases. In one aspect the invention relates to method and apparatus for the recovery of helium from a helium-containing gas. in a further aspect the invention relates to a control system for utilization in the recovery of helium from natural gas. in a still further aspect the invention relates to method and apparatus for controlling the separation of gases.

The value of helium as an inert atmosphere, a cornponent of an artificial breathing medium, a lifting gas, and other diverse uses has been known. The world supply of naturally-available helium is limited to very few geographical locations, most of which are within the continental United States, and is further limited so far as is presently known as being a minor constituent of natural gas. Various efforts have been made in the past to recover the helium from such a gas mixture economically, and have met with greater or lesser success.

When the constituents of a liquid are separated by flash distillation, a more distinct separation is obtained if the liquid is flashed in stages. However it is dicult to control the flow of liquid from one stage to another and to remove the vapor from each stage without overloading the compressors which compress the vapors. En the past it has been proposed to utilize a liquid level controller to regulate the rate of withdrawal of liquid from a phase separator and to utilize a pressure controller to regulate the rate of withdrawal of vapor from the phase separator to thereby maintain the phase separator under the desired equilibrium conditions. While such a control system is generally satisfactory where the process is not subject to a wide variation in operating conditions, this system of controls does not perform satisfactorily under abnormal operating Vconditions such as start-up operations and failure of other controls in the process. The problem becomes acute when the liquid withdrawn from the phase separator is passed in heat exchanging relationship with the incoming feed to aid in cooling the feed to condense a portion thereof. For example under a condition which results in an excessive drop in liquid level in the phase separator, the control system would function by closing the valve in the liquid withdrawal line, resulting in an increase in pressure in the phase separator, thereby causing the pressure controller to open the valve in the vapor withdrawal line even wider. The reduction or elimination of the withdrawal of liquid from the phase separator results in less heat being removed from the incoming feed, causing the ratio of vapor to liquid in the feed entering the phase separator to increase even farther. The occurrence of such an abnormal condition can result in the complete shut down of a process utilizing such a control system.

In accordance with the present invention it has been discovered that these difficulties can be overcome by utilizing a plurality of phase separators in series with the liquid withdrawn from each phase separator, other than the last phase separator, being introduced into the next phase separator in the series at a rate controlled responsive to the differential pressure between the two respective phase separators, while the vapors are withdrawn from each phase separator at a rate controlled responsive to the liquid level in the respective phase separator. In a presently preferred embodiment the vapor streams are combined, with each individual stream, other than the stream from the last phase separator, being controlled responsive to the liquid level in the respective phase separator, and the combined stream flow rate is controlled responsive to the liquid level in said last phase separator.

Accordingly, it is an object of this invention to provide a method and apparatus for separating a gas mixture. It is another object of this invention to provide economical method and apparatus for recovering helium from a gas mixture containing helium. It is a further object of the invention to provide improved method and apparatus for the recovery of various constituents from natural gas, such as natural gas liquids, helium, and nitrogen. It is a further object of this invention to provide method and apparatus for the separation of various constituents of natural gas without requiring external refrigeration. Yet another object of the invention is to provide an improved control system for utilization in the recovery of one or more components from natural gas. A still further object of the invention is to provide a new control system for the recovery of helium from natural gas. Another object of the invention is to provide method and apparatus for controlling a process for separating a gas mixture.

Gther aspects, objects and advantages of the invention will be apparent from a study of the disclosure, the drawing and the appended claims to the invention.

Referring now to the drawing there is shown a diagrammatic representation of a helium recovery system utilizing the present invention. A feed stream comprising helium, nitrogen and C1 to C5 hydrocarbons is compressed in compressor 10 and passed through line 11 into and through ow path l2 of heat exchanger 13 wherein the feed stream is substantially cooled. The thus cooled feed stream is passed through line 1.4 into phase separator 15. The condensed liquid which is predominantly C1 to C5 hydrocarbons with a small amount of nitrogen, is withdrawn from phase separator i5 by way of line 16 and passed into and through flow path 17 of heat exchanger 13 in heat exchanging relationship with additional feed in line ll to recover the refrigeration power contained in the condensed liquid. The heated fluid leaving flow path i7 is withdrawn from the process by way of line 18 as a rich gas. rThe rate of flow through line 16 can be controlled to maintain the liquid level in separator 15 substantially constant by means of valve i9 which is actuated by liquid level controller al responsive to the liquid level in separator l5. The vapors, which comprise substantially all of the helium and the major portion of the nitrogen contained in the feed stream with the remainder being primarily C1 hydrocarbons with a small amount of C2 to C4 hydrocarbons, are withdrawn from separator 15 by way of line 22 and passed into and through flow path 23 of heat exchanger 24 wherein the vapors are further cooled. The thus cooled vapors are passed by way of line 25 into phase separator 26. The condensed liquid is withdrawn from phase separator 26 and introduced into phase separator 27 by way of line 2S at a rate responsive to the differential pressure between phase separators 26 and 27 by means of valve 29 which is actuated by differential pressure controller 3i. The vapors are withdrawn from phase separator 26 and passed by way of line 32 into line 33 at a rate responsive to the liquid level in phase separator 26 by means of valve 34 which is actuated by liquid level controller 35. The vapors' which are flashed in phase separator 27 are withdrawn therefrom and passed by way of line 36 into line 33 at a rate responsive to the liquid level in phase separator 27 by means of valve 37 which is actuated by liquid level controller 38. Liquid is withdrawn from phase separator 27 and passed by way of line 39 into phase separator 4l at a rate responsive to the differential pressure between phase separator 27 and phase separator el by means of valve 42 which is actuated by differential pressure controller 43. The vapors which are ashed in phase separatorV 41 are withdrawn therefrom and passed by way of line 44 into line 33 at a rate responsive to the liquid level in phase separator 41 by separators 26, 27, 41 and 48 with the vapor section of separators 27, 41, 48 and 56, respectively. PipesV 81, 82, 83 and 84 are restricted so that about thirty percent of the liquid which is passed from one stage to another goes means of valve 45 which is actuated by liquid level con- 5 through the respective pipe. Pipes 81, 82, 83 and 84 are troller 46. provided to prevent the buildup in one of the upper cham- Liquid is withdrawn from phase separator 41 and passed bers of a higher pressure than the next lower chamber as by way of line 47 into phase separator 48 at a rate rethe walls between the chambers aredesigned to have their sponsive to the differential pressure between phase sepmaximum strength in the direction of a greater pressure arator 41 and phase separator 48 by means of valve 49 10 in each chamber than the pressure in the next higher which is actuated by dierential pressure controller 51. chamber.

The vapors flashed in phase separator 48 are withdrawn When operating with a control system in accordance therefrom and passed by way of line 52 into line 33 at with the present invention, the flow of liquid from stage a rate responsive to the liquid level in phase separator 48 to stage will be adequate even in the event of system upby means of valve 53 which is actuated by liquid level 15 sets to keep from overloading the compressor 10. Thus controller 54. Liquid is withdrawn from phase separator when the liquid level increases above the predetermined 48- and passed by way of hne 55 into phase separator 56 desired value, the valve in the corresponding vapor withat a rate I'eSpOnSiVe t0 the differential pressure between drawal line Closes a Corresponding amount, causing an phase separator 48 and phase separator 56 by means of increase in pressure in the phase separator, resulting in valve 57 which is actuated by -dlfferentlal pressure con- 20 an increase in diierential pressure between that phase septroller 58. The vapors flashed 1n phase separator 56 are arator and next phase separator in the series, which in withdrawn therefrom and. passed by Way o f llne 59 Into turn causes the valve in the liquid withdrawal line for the line l33. While 1t 1s within the Contemplatlon 0f the 111- particular phase separator to be opened further, thus revennpn to control the rate of flow of vapors through llne sulting inran increase in liquid withdrawal rate and a drop 59 d1rect1y re.spons1ve to the l1qu1d level m phase Sep- 25 in liquid level. This increase in the pressure in the phase al'aOr 56, 1l 1S Preserl'fly` Preferred t0 eoh'frOl the .tetffll separator provides a greater driving force to cause liquid llOW ef VaPOrs through lrhe 33 resPC'rlslVe t0 the llqlhd to how faster into the next phase separator. When the leVel 1h Phase seP-rhlor 56 hy rrleahs 0f Valve 61 Whleh liquid level in a particular phase separator drops below a 1S aelhated by llflhld leVel Controller 62.- The VaPOrS predetermined desired value, the valve in the correspond- Passlhgthrohgh hhe 33 and Valye 61 are lh'fl'odueed 1h10 30 ing vapor withdrawal line opens further, the dierential sePsrahOh Zohe 63 for fhrlher sePara'rlOh- A Crude pressure decreases, the valve in the corresponding liquid hellllm Stream 1s recovered 1h seParahOh Zohe 63 and withdrawal line is closed further, thus decreasing liquid Passed hy Way 0f hhe 64 lhO hd through flOW Path 65 withdrawal rate, resulting in an increase in liquid level.

0f heal exchanger 13 60 reCOVer the COO'llhg POWer C011- Phase separator 15 is described with a conventional tamed 111 the Crude hellllrh stream, and 1s remOVeCl from 35 liquid level controller 21 on the liquid withdrawal line 16, the Pr0Cess by Why O f llhe 66 A fuel gas Stream 1s also as the amount of liquid removed in separator 15 is small recovered 111, SeParahOIl ZOrle 63 and Passed by Way 0f and the system downstream of separator 15 is capable of lllle 67 lhtO and thrOhgh lOW Path 68 0f heat eXehahgel' handling the extra amount if the control system fails. 24 and then by Way 0f hhe 62 1hr? ahd thl'Ohgh hOW Path However it is within the contemplation of the invention 71 0f hear exchanger 13 and ls WlthdraWh from the Proc 40 to control the liquid withdrawal rate from separator 15 eSS hy Way Of .llne 72- responsive to the pressure in separator 15 where the Llquld 1s WlthdraWh frf'hh Phase separator '56 hy Way 0f amount of liquid removed therein is larger than. the relme 73 at a fate reSPOrlslVe 'l0 the Pressure h1 Phase seP mainder of the system can accept under overload conarator 56 by means of valve 74 wh1ch 1s actuated by ditlons,

pressure recorder controller 75. The l1-qu1d 1n 11ne- 73 1s 45 The following example is presented in further illustra- Passed luto and though 110V/ Path 76 m heat exchanger tion of the invention but is not tobe construed unduly 24 and then through hne 77 into and through how path in limitation thereof.

78 in heat exchanger 13 wherein it is vaporized to recover the cooling power. The vaporized euent from flow path EXAMPLE I 78 is withdrawn from the process by way of line 79. 50 l In a presently preferred embodiment phase separators A System 1h accordance Wlth 'rhedraWlhg'fOr 1'-he re- 26, 27, 41, 48A and 56 are constructed in the form of a covery of helium, a fuel gas, a residue gas, and heavy single column, and restricted pipes 81, 82, 83 and 84 are hydrocarbons is operated under the conditions and with provided in communication between the liquid section of the results set forth in the following tables.

Table I Pressure, Temper- Flow Molecular Stream Phase He N3 C1 C1 Ca O1 C5 p.s.i.g. ature, Rate, Weight F. M01/Hr.

V .623 12.037 74.260 6.514 4.184 1.654 728 350 +90 100 20.60 V 62268 11.93487 70.94326 3.86041 .85602 .04791 345 L 00032 .10213 3.31674 2.65359 3.32798 1.60609 .728 345 v 00032 .10019 3 306587 .54411 05956 3 L .00194 25087 2.10948 3 26842 1.60609 .72s 30 V 00032 .10213 3.31674 2.65359 3.32798 1.60609 .728 20 V 62268 11.93487 70.94326 3.86041 .85602 .04791 345 v 48813 1.70768 2.10111 .00294 00005 335 L 13455 10.22719 68.84215 3 85747 85597 .04791 335 V 62168 4.60631 5.60791 01074 00013 235 V 62164 .49018 00856 386 V .62164 .49018 00856 380 v 00002 4.04740 5 59810 01074 00013 75 V 00002 4.04740 5. 59810 .01074 00013 73 V 00002 4.04740 5.59810 .01074 .00013 70 L 00100 7.32856 65.33535 3.84967 .85589 235 v .00100 7.32856 65.33535 3.84967 .85589 227 -922 77.14838 18.21 V .00100 7.32856 65.33534 3.94967 .85589 219 +80 77.41838 18.21

1 Downstream of valve 19.

As noted above, the drawing is merely diagrammatic and is not intended to fully show all component parts of the equipment which one sldlled in the art will routinely design for the operation. lndeed, the showing of an element or piece of equipment does not mean that all such or similar pieces of equipment which may or can be designed by one skilled in the art in possession of this disclosure cannot be utilized as substitution therefor, likewise, the omission of an element which one skilled in the art may include in an actual unit does not mean that such a piece of equipment is intended to be omitted simply because it does not appear in the drawing. Sulice to say, the drawing is for illustrative purposes, as is the description thereof.

Reasonable variation and modication are possible within the scope of the foregoing disclosure, the drawing and the appended claims to the invention.

I claim:

l. A process for separating a component from a mixture containing said component comprising cooling said mixture, introducing the thus cooled mixture into a first separation zone, withdrawing liquid from said rst separation zone, introducing the thus withdrawn liquid into a second separation zone at a rate responsive to the dilerence in pressure between said rst and second separation zones, withdrawing vapor from said rst separation Zone at a rate responsive to the liquid level in said iirst separation zone, withdrawing vapor vfrom said second separation zone at a rate responsive to the liquid level in said second separation zone, and withdrawing liquid from said second separation zone responsive to the pressure in said second separation zone.

2. A process for separating a component from a mixture containing said component comprising cooling said mixture to condense a portion thereof; introducing the thus cooled mixture into the rst one of a plurality of separation zones which are arrayed in series; withdrawing liquid from each of said plurality of separation zones, other than the last one of said plurality of separation zones, and introducing the thus withdrawn liquid into the next one of said plurality o separation zones responsive to the differential pressure between the separation zone from which the liquid is withdrawn and the separation zone into which the thus withdrawn liquid is introduced; removing liquid from said last one of said plurality of separation zones responsive to the pressure in said last one of said plurality of separation zones, and passing the thus removed liquid into heat exchmging relationship with additional mixture to thereby cool said additional mixture; withdrawing vapors from each of said plurality of separation zones at a rate responsive to the liquid level in the respective separation zone; and passing the thus withdrawn vapors into heat exchanging relationship with said additional mixture to aid in cooling said additional mixture; each of said plurality of separation zones bein maintained at a lower pressure and a lower temperature than the preceding one of said plurality of separation zones when considered in the order of said first one to said last one.

3. A process in accordance with claim 2 wherein said thus withdrawn vapors are combined and subjected to further separation procedures before being passed in heat exchanging relationship with said additional mixture.

4. A process for obtaining a helium concentrate stream from a natural gas containing helium which comprises cooling said natural gas in a Erst heat exchange zone to condense a portion of the heavy hydrocarbons contained in said natural gas; separating the resulting liquid from the thus cooled natural gas; passing the remaining gases through a second heat exchange zone to further cool said remaining gases; introducing the thus further cooled gases into the rst one or" a plurality of separation zones which are arrayed in series; withdrawing liquid from each of said plurality of separation zones, other than the last one of said plurality of separation zones, and introducing the thus withdrawn liquid into the next one of said plurality of separation zones responsive to the diierential pressure between the separation zone from which the liquid is withdrawn and the separation zone into which the thus Withdrawn liquid is introduced; removing liquid from said last one of said plurality of separation zones responsive to the pressure in said last one of said plurality of separation Zones, and passing the thus removed liquid into heat exchanging relationship with additional natural gas in said iirst and second heat exchange zones to thereby cool said additional natural gas; withdrawing vapors from each of said plurality ot separation zones at a rate responsive to the liquid level in the respective separation Zone; and passing the thus withdrawn vapors into heat exchanging relationship with said additional natural gas in said iirst and second heat exchange zones to aid in cooling said additional natural gas; each of said plurality of separation Zones being maintained at a lower pressure and a lower temperature than the preceding one of said plurality oi separation zones when considered in the order of said first one to said last one.

5. A process in accordance with claim 4 wherein said thus withdrawn vapors are combined and then separated into a helium concentrate stream and a fuel gas stream before being passed in heat exchanging relationship with said additional natural gas.

6. A process in accordance with claim 5 wherein the rate of withdrawal of vapors from said last one of said plurality of separation zones is controlled by manipulating the rate of ow ot the stream or combined vapors responsive to the liquid level in said last one of said plurality ot separation zones.

7. Apparatus for separating a component of a mixture containing said component comprising means for cooling said mixture to condense a portion thereof; a plurality of phase separators arrayed in series; means for introducmg the thus cooled mixture into the rst one of said plurality of phase separators; means associated with each of said phase separators for withdrawing liquid therefrom; means for introducing the thus withdrawn liquid from each of said phase separators other than the last one of said phase separators in said series into the next one of said plurality of said phase separators in said series at a rate reponsive to the differential pressure between the phase separator from which the liquid is withdrawn and the phase separator into which the thus withdrawn liquid is introduced; means for passing the withdrawn liquid from said last one of said plurality of said phase separators into indirect heat exchanging relationship with an additional portion of said mixture at a rate responsive to the pressure in said last one of said plurality of said phase separators; and means connected to each of said plurality of phase separators for withdrawing vapors from each of said plurality of said phase separators at a rate responsive to the liquid level in the respective phase separator.

8. Apparatus in accordance with claim 7 further comprising means for combining the vapors withdrawn from each of said plurality of phase separators and means for passing the thus combined vapors into indirect heat exchanging relationship with an additional portion of said mixture.

9. Apparatus for obtaining a helium concentrate stream from a natural Uas containing helium which comprises a fust indirect heat exchanger, means for passing said natural gas through said rst heat exchanger, a plurality of phase separators arrayed in series; means for introducing into the first one in the series of said plurality of phase separators the cooled natural gas from said iirst heat exchanger, means associated with each of said plurality of phase separators to Withdraw liquid therefrom, means for passing the liquid withdrawn from each of said plurality of said phase separators other than the last one in the series of said phase separators to the next phase separator in said series at a rate responsive to the diierential pressure between the phase separator from which the liquid is withdrawn and the phase separator into which the liquid is introduced, means for passing the liquid withdrawn from said last one in the series of said phase separators in indirect heat exchanging relationship with an additional portion of said natural gas in said first heat exchanger at a rate responsive to the pressure in said last one in a series of said plurality of phase separators, means associated with each of said plurality of phase separators for withdrawing vapors therefrom, means for controlling the rate of withdrawal of vapors from each of said plurality of phase separators other than the last one of said phase separators at a rate responsive to the liquid level 8.. in the respective phase separator, means for combining the thusrwithdrawn vapors, means for controlling the rate of ow of the thus combined vapors responsive to the liquid level in said last one of said plurality of phase separators, means for separating said combined vaporsV into a crude helium stream and a fuel gas stream, means for passing saidcrude helium stream and the said fuel gas stream through said first heat exchanger in indirect heat exchanging relationship with additional natural gas.

References Cited in the iile of this patent UNITED STATES PATENTS 1,664,412 Haynes Apr. 3, 1928 2,389,244 Whaley NOV. 20, 1945 2,606,863 Rehbein Aug. 12, 1952 2,743,998 Swart May l, 1956 2,786,703 Parks Oct. 30, 1956 2,882,693 Clay Apr. 21, 1959 3,026,682 Palazzo et al Mar. 27, 1962 3,034,307 Berger May l5, 1962 3,073,130 Becker Jan. l5, 1963 

1. A PROCESS FOR SEPARATING A COMPONENT FROM A MIXTURE CONTAINING SAID COMPONENT COMPRISING COOLING SAID MIXTURE, INTRODUCING THE THUS COOLED MIXTURE INTO A FIRST SEPARATION ZONE, WITHDRAWING LIQUID FROM SAID FIRST SEPARATION ZONE, INTRODUCING THE THUS WITHDRAWN LIQUID INTO A SECOND SEPARATION ZONE AT A RATE RESPONSIVE TO THE DIFFERENCE IN PRESSURE BETWEEN SAID FIRST AND SECOND SEPARATION ZONES, WITHDRAWING VAPOR FROM SAID FIRST SEPARATION ZONE AT A RATE RESPONSIVE TO THE LIQUID LEVEL IN SAID FIRST SEPARATION ZONE, WITHDRAWING VAPOR FROM SAID SECOND SEPARATION ZONE AT A RATE RESPONSIVE TO THE LIQUID LEVEL IN SAID SECOND 